Large amounts of petroleum-based plastics are disposed of every year, and serious problems caused by the large amounts of wastes, such as shortage of landfills and environment pollution, have been discussed. Under the circumstances, biodegradable plastics have been drawing attention since biodegradable plastics are degraded by the action of microorganisms in the environment, landfills, or composts. Biodegradable plastics are under development with the aim of expanding their application to materials for use in the environment in agriculture, forestry, and fisheries, and also to food containers, packaging materials, sanitary materials, and garbage bags, which are difficult to recover/recycle after use.
Among them, from the viewpoint of reducing carbon dioxide emission or carbon dioxide fixation (carbon neutral), polyhydroxyalkanoates (hereinafter, abbreviated as “PHA” in some cases), which are plant-derived aliphatic polyesters, have been drawing attention. Among polyhydroxyalkanoates, in particular, polylactic acids (hereinafter, abbreviated as “PLA” in some cases) have been drawing attention because lactic acid, which is the raw material of the polylactic acids, is inexpensive for the reason that it is produced by fermentation using sugars that are extracted from corn, potato, or the like, and also because PLA resins are highly rigid and highly transparent.
However, the glass-transition temperature of such a polylactic acid is around 55° C. Therefore, the thermal resistance of the polylactic acid is insufficient and the application thereof is limited. In addition, since the crystallization speed of the polylactic acid is slow, even if the polylactic acid is kept around 100° C. at which its crystallization is most facilitated, it takes a long period of time to complete the crystallization, resulting in poor productivity. In order to improve the thermal resistance and processability, there is proposed a method of mixing a polylactic acid resin with another resin and a soluble azo lake pigment serving as a crystal nucleating agent (Patent Literature 1).